1) Field of the Invention
The present invention relates generally to flow sensors for harvestors, and more specifically, to an improved microwave flow sensor for a harvestor.
2) Related Art
Different attempts have been made at means and methods for detecting flow rates in harvesters. These attempts are discussed in the context of measuring flow rate of cotton on a cotton harvester, but at least some of the same problems are present in the harvesting of other types of crops. One problem with other flow rate sensors, including flow rate sensors that may use microwave signals, is the accuracy of the measured flow rate. This can be particularly important in precision agriculture applications or other applications that may require an accurate measurement of the flow rate of cotton or grain. For example, in precision agriculture applications such as yield monitoring and mapping, it is crucial to have accurate measurements of yield. As yield rates can be computed from flow rates, it is crucial to have accurate flow rates.
Another problem with the flow rate measurements in prior art devices is that differences in the velocity of the flow in material cause the measured flow rate to deviate from the actual flow rate. One cause of these differences in the velocity of flow is the lack of uniformity in air velocity from one duct to the next, a duct being the structure through which harvested material flows.
Yet another problem with prior art sensors is that they often require periodic calibration to compensate for drift. This drift includes changes in the velocity of the flowing material.
A further problem with prior art flow sensors used in harvestors is inaccuracy due to the effect of stationary vibrating surfaces. Due to vibrations, such as when a flow sensor is used to measure the flow of a material in a duct on a harvester, there are inaccuracies in the detection of the moving material. Some methods convert time domain information to the frequency domain. In these prior art applications, one prior art method of overcoming this problem of vibration has been to set an arbitrary cut off frequency to separate the effects of the stationary vibrating surfaces from those of moving cotton. This creates inaccurate measurements when the spectra of the flowing material and that of the machine vibrations overlap.
A problem with prior art cotton flow sensors is that using a cotton flow sensor in close proximity to dry cotton can result in damage to the electronic components of the sensor due to high electric fields that are sometimes generated around the duct in dry conditions as the flowing cotton rubs inside of the duct. Therefore problems remain, and there is a need for an improved cotton flow sensor.
It is therefore an object of the present invention to provide an improved harvester flow sensor that improves upon the state of the art.
It is another object of the present invention to provide a harvestor flow sensor that provides accurate and consistent flow measurement.
It is a further object of the present invention to provide a cotton flow sensor that allows sufficient separation between electronic components and cotton flow that the high electric fields sometimes generated by flowing cotton and dry conditions do not damage the electronic components.
A further object of the present invention is to provide a flow sensor that compensates for variations in the velocity of the flowing material.
Yet another object of the present invention is to provide a harvestor flow sensor that is not impaired by the effects of stationary vibrating surfaces.
A still further object of the present invention is to provide a flow sensor suitable for use on a harvester.
A harvester flow sensor of the present invention permits the sensing of flow rate of cotton, grain or other crops within a duct of a harvester. The flow sensor includes a microwave transceiver attached to the harvester for transmitting a microwave signal and receiving a reflected microwave signal. An in-phase mixer is electrically connected to the microwave transceiver for combining the transmitted microwave signal and the reflected microwave signal, and outputting an in-phase Doppler signal. A quadrature mixer is electronically connected to the microwave transceiver for combining the transmitted microwave signal and a delayed reflected microwave signal and outputting a quadrature Doppler signal. The present invention also provides for filtering the DC components of the Doppler signals. By filtering and sampling these components, transmit power variations and in-phase and quadrature channel differences are compensated for.
An electronic circuit is electrically connected to the filtered outputs of the in-phase mixer and the quadrature mixer and has a flow rate output. The electronic circuit may contain a digital signal processor which includes instructions for sampling the in-phase Doppler signal and the quadrature Doppler signal and computing a Fast Fourier Transform.
The Fast Fourier Transform is computed on the set of complex numbers formed from the combination of the samples of the in-phase Doppler signal and the quadrature Doppler signal in order to produce a frequency domain spectrum having corresponding amplitude components and phase components. From this amplitude spectrum a power spectrum is computed. By multiplying the power components with their corresponding frequencies, a flow rate is calculated.
In this manner the present invention provides advantages that include accuracy and consistency of flow rate measurements.